1. Field of the Invention.
The present invention relates to a method for patching or sealing leaks in fluid systems and, in an exemplary application, relates to a method for patching or sealing leaks in hydraulic fluid control systems of the type which are used in oil and gas production applications, such as leaks in sub-sea hydraulic control lines, leaks in sub-surface or sub-sea safety valves, O-ring leaks of any type, leaks in hydraulic line fittings, tubing thread connection leaks, casing thread connection leaks, glycol hydraulic system leaks, well-head and sub-sea well-head leaks, hanger leaks, and leaks in other types of related down-hole equipment, for example.
2. Description of the Related Art.
In the oil industry, offshore oil platforms are used to extract oil from oil reservoirs located within continental shelves beneath the sea floor, and to convey the extracted oil to the ocean surface. Typically, an oil platform is positioned above the sea floor, and one or more wells, complete with all the necessary components to operate in the sub-sea environment, is installed on the sea floor. The well includes apparatus for extracting oil from oil reservoirs beneath the sea floor, and is equipped with a hydraulically controlled down-hole safety valve. The well is used to convey the oil upwardly to a production facility. A hydraulic fluid control system is commonly used to control the operation of the sub-sea components and down-hole safety valves, and includes a series of hydraulic control lines extending from a control apparatus on the platform downwardly to a hydraulic control pod associated with the sub-sea installation on the sea floor, or directly to the safety valve in an above surface well-head. The hydraulic control lines are used to operate valves and other controls on the sub-sea installation or down-hole. The hydraulic control lines are typically approximately ¼″ (0.635 cm) in inside diameter, and may be arranged in bundles which extend from the platform or production facility to the sub-sea installation.
Problematically, it has been observed that leaks frequently develop in the high pressure hydraulic control lines, in the fittings which connect the control lines to other system components, or anywhere else in the production system. It is estimated that the hydraulic control systems of offshore oil platforms around the United States alone may have thousands of such leaks. Although such leaks are typically small, the high pressure of the hydraulic fluid within the control systems potentially leads to a large amount of total leakage of hydraulic fluid into the ocean, affecting the proper functioning of the system and risking possible environmental contamination, especially when the control systems are operated continuously for long periods of time. Problematically, once such hydraulic control systems are operational, identifying individual leaks in the systems is very difficult. Even if a leak is identified, shutting the hydraulic control system down to retrieve and repair system components is at best extremely difficult and expensive, and is at worse almost impossible.
One known method for patching leaks which occur in oil well casings, for example, is described in U.S. Pat. Nos. 5,954,132 and 6,105,673, each to Harris et al., the disclosures of which are expressly incorporated herein by reference. In this method, two reactive aqueous liquids are pressure injected into an annulus formed between a well casing and a concentric tubing. The fluids react with one another to yield a solution having liquid and solid phase materials, and the liquid phase materials are pressed from the solid phase materials to deposit a filter cake on the casing at the leak site to patch the leak.
Although the foregoing method has proven to be very effective for patching leaks in oil well casings, for example, it is contemplated that such method would not be as effective or suitable for patching the relatively small sized leaks which frequently occur in hydraulic control systems for risk of plugging the small diameter lines of such systems. Additionally, the abrasiveness of the crystalline materials produced in the foregoing method could potentially result in ineffective patching of many types of leaks which occur in hydraulic control systems, such as leaks associated with fittings and valves having defective O-rings, for example.
U.S. Pat. No. 4,487,707 to Holzknecht discloses a leak sealing composition and method for refrigeration systems. A leak sealing composition is disclosed which includes one part graphite particles, one part polytetrafluoroethylene (“PTFE”) particles, and five parts mineral oil, for example. Although PTFE particles are disclosed, however, Holzknecht states that “graphite particles alone suspended in refrigeration oil are effective as a leak sealant” (col. 3, lines 48 and 49), and only graphite particles and refrigeration oil are used in the working examples (col. 4, line 30 through col. 5, line 31). The composition is disclosed as useful for sealing holes in metal components up to about 0.015 inch in diameter, as well as voids in gasketed or O-ring type joints up to about 0.008 inches (col. 3, lines 24-30).
Suitable PTFE particles are disclosed as being available from Custom Compounding, Inc., under the name Polylube® in the form of elongated particles in the range of 20 to 50 microns or 20 microns to 65 mesh. PTFE particles of the foregoing type are known in the art as micropowders, or granular PTFE particles, and are produced by a known suspension polymerization processes. Referring to FIG. 1, Holzknecht states that “[a]dvantageously, particles 14 and 15 of the invention will tend to be forced out through the pinhole by the internal pressure. We have found experimentally that particles 14 and 15 will agglomerate and under continued pressure will agglutinate to fill the pinhole, thereby preventing further leakage of the refrigerant 12”. (col. 3, lines 15-21).
Thus, the method of Holzknecht employs micropowders of PTFE particles, such as the disclosed Polylube® product, which are typically available in solid form, and may be suspended in a viscous carrier medium such as oil and/or glycol for use as a lubricant, for example. When in solid form, it is known that the individual PTFE micropowder particles tend to agglomerate, or clump together, to form agglomerated functional particles which are much larger than their nominal particle size. It is believed that the mechanism by which such micropowders effect a seal at a leak site is by agglomerating or agglutinating with one another to close or seal the leak by physically “bridging” the leak site without the particles themselves undergoing a physical change at the level of the individual particles. This effectively limits the size of leaks which can be sealed using PTFE particles in micropowder form and/or graphite particles. For example, in “Test No. 1” of Holzknecht, a composition including “2 ounces of 525 VIS refrigeration oil having 1.5 parts #A-60 graphite particles and 1.5 parts 4110 particles” was unable to seal a relatively small leak in a refrigeration system which was formed with a 0.027 inch needle.
What is needed is a method for patching leaks in fluid systems, particularly in hydraulic control systems, which is an improvement over the foregoing.